JP2011228052A - Lithium ion secondary battery - Google Patents

Lithium ion secondary battery Download PDF

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JP2011228052A
JP2011228052A JP2010095097A JP2010095097A JP2011228052A JP 2011228052 A JP2011228052 A JP 2011228052A JP 2010095097 A JP2010095097 A JP 2010095097A JP 2010095097 A JP2010095097 A JP 2010095097A JP 2011228052 A JP2011228052 A JP 2011228052A
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lithium
positive electrode
negative electrode
secondary battery
ion secondary
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JP5099168B2 (en
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Naoto Yasuda
直人 安田
Toru Abe
徹 阿部
Junichi Niwa
淳一 丹羽
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Toyota Industries Corp
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Priority to CN201180012997.7A priority patent/CN102792509B/en
Priority to US13/581,355 priority patent/US20120321955A1/en
Priority to PCT/JP2011/001980 priority patent/WO2011129066A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/387—Tin or alloys based on tin
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery of which battery capacity hardly decreases even if usage of an active material is more decreased than conventional usage.SOLUTION: A lithium ion secondary battery comprises: a positive electrode containing a positive electrode active material including lithium-transition metal composite oxide including at least lithium and manganese and having a lamellar rock salt structure; a negative electrode containing a negative electrode active material including at least one of a carbon-based material, a silicon-based material and a tin-based material; and a nonaqueous electrolyte. The lithium-transition metal composite oxide has irreversible capacity, and actual capacity of the negative electrode to metal lithium at initial charging by 0 V is below actual capacity of the positive electrode to metal lithium at initial charging by 4.7 V.

Description

本発明は、リチウムイオン二次電池に関するものである。   The present invention relates to a lithium ion secondary battery.

近年、携帯電話やノート型パソコンなどのポータブル電子機器の発達や、電気自動車の実用化などに伴い、小型軽量でかつ高容量の二次電池が必要とされている。現在、この要求に応える高容量二次電池としては、正極材料としてコバルト酸リチウム（ＬｉＣｏＯ２）、負極材料として炭素系材料、を用いた非水二次電池が商品化されている。このような非水二次電池はエネルギー密度が高く、小型化および軽量化が図れることから、幅広い分野で電源としての使用が注目されている。しかしながら、ＬｉＣｏＯ２は希少金属であるＣｏを原料として製造されるため、今後、資源不足が深刻化すると予想される。さらに、Ｃｏは高価であり、価格変動も大きいため、安価で供給の安定している正極材料の開発が望まれている。 In recent years, along with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, secondary batteries with small and light weight and high capacity are required. Currently, non-aqueous secondary batteries using lithium cobaltate (LiCoO 2 ) as a positive electrode material and a carbon-based material as a negative electrode material are commercialized as high capacity secondary batteries that meet this requirement. Such a non-aqueous secondary battery has a high energy density, and can be reduced in size and weight, so that it is attracting attention as a power source in a wide range of fields. However, since LiCoO 2 is manufactured using Co, which is a rare metal, as a raw material, it is expected that a shortage of resources will become serious in the future. Furthermore, since Co is expensive and has a large price fluctuation, development of a positive electrode material that is inexpensive and stable in supply is desired.

そこで、構成元素の価格が安価で、供給が安定しているマンガン（Ｍｎ）を基本組成に含むリチウムマンガン酸化物系の複合酸化物の使用が有望視されている。その中でも、４価のマンガンイオンからなり、充放電の際にマンガン溶出の原因となる３価のマンガンイオンを含まないＬｉ２ＭｎＯ３という物質が注目されている。 Therefore, the use of a lithium manganese oxide-based composite oxide containing manganese (Mn), whose constituent elements are inexpensive and whose supply is stable, is considered promising. Among them, a substance called Li 2 MnO 3 that is composed of tetravalent manganese ions and does not contain trivalent manganese ions that cause manganese elution at the time of charge and discharge has attracted attention.

ところで、ＬｉＣｏＯ２やＬｉ２ＭｎＯ３などの酸化物は、炭素に比べて金属リチウムに対する電極電位が高い。つまり、これらの酸化物を正極材料、炭素系材料を負極材料としてリチウムイオン二次電池を構成する場合、たとえば長期間の使用により炭素系材料が劣化すると、負極が炭素の理論容量を超えて負極表面にリチウムが析出しやすくなる。そこで、安全性の観点から、リチウムの析出を防止するために正極容量よりも負極容量を大きくするのが通常である。そしてこの場合、二次電池の容量は、容量の小さい正極の容量に応じて決定（正極規制）される。 By the way, oxides such as LiCoO 2 and Li 2 MnO 3 have a higher electrode potential with respect to metallic lithium than carbon. In other words, when a lithium ion secondary battery is configured using these oxides as a positive electrode material and a carbon-based material as a negative electrode material, for example, if the carbon-based material deteriorates due to long-term use, the negative electrode exceeds the theoretical capacity of carbon and the negative electrode Lithium tends to precipitate on the surface. Therefore, from the viewpoint of safety, in order to prevent lithium deposition, it is usual to make the negative electrode capacity larger than the positive electrode capacity. In this case, the capacity of the secondary battery is determined (positive electrode regulation) according to the capacity of the positive electrode having a small capacity.

一方、特許文献１には、保存性の向上の観点から、正極の容量よりも負極の容量を小さくした、負極規制のリチウムイオン二次電池が開示されている。この二次電池は、正極の容量よりも負極の容量を小さくすることで、充電時に正極から放出するリチウムの割合を制限している。その結果、負極電位の低下に伴う炭素と電解液との反応による被膜の形成が抑制され、また、正極活物質の結晶構造の崩壊が抑制されて、充電状態での保存性が向上する。   On the other hand, Patent Document 1 discloses a negative electrode-regulated lithium ion secondary battery in which the capacity of the negative electrode is smaller than the capacity of the positive electrode from the viewpoint of improving the storage stability. This secondary battery limits the proportion of lithium released from the positive electrode during charging by making the negative electrode capacity smaller than the positive electrode capacity. As a result, the formation of a film due to the reaction between carbon and the electrolyte accompanying a decrease in the negative electrode potential is suppressed, and the collapse of the crystal structure of the positive electrode active material is suppressed, so that the storage stability in the charged state is improved.

特表２００２−１５１１５４号公報Special Table 2002-151154

特許文献１では、正極容量よりも負極容量を小さくすることで、負極の体積を小さくできると記載されている。そして、負極活物質として使用される炭素系材料は、リチウムマンガン複合酸化物よりも比重が小さいため、体積の減少効果は大きく、電池の体積エネルギー密度が高くなると述べている。しかしながら、特許文献１に記載の電池はいわゆる「負極規制」となるため、初期電池容量が小さくなるという欠点を有する。   Patent Document 1 describes that the negative electrode volume can be reduced by making the negative electrode capacity smaller than the positive electrode capacity. The carbon-based material used as the negative electrode active material has a specific gravity smaller than that of the lithium manganese composite oxide, so that the volume reduction effect is large and the volume energy density of the battery is increased. However, since the battery described in Patent Document 1 is a so-called “negative electrode regulation”, it has a drawback that the initial battery capacity is reduced.

本発明は、活物質の使用量を従来よりも低減させても、電池容量がほとんど低下しないリチウムイオン二次電池を提供することを目的とする。   An object of the present invention is to provide a lithium ion secondary battery in which the battery capacity hardly decreases even when the amount of active material used is reduced as compared with the conventional one.

リチウムイオン二次電池の電池容量は、これまで、リチウムイオンの移動により生じると考えられてきた。したがって、充電により正極から移動したリチウムイオンが負極に吸蔵されたまま移動しなくなることで、不可逆容量が発生すると考えられてきた。ところが、本発明者等が正極活物質としてのＬｉ２ＭｎＯ３の充放電特性を調査した結果、初回の充電によりＬｉ２ＭｎＯ３からリチウムイオン以外の陽イオンが負極に移動していることがわかった。これは、Ｌｉ２ＭｎＯ３からなる正極活物質を含む正極とグラファイトからなる負極とでリチウムイオン二次電池を組み立てた場合に、初回の充電後の負極（炭化リチウム）のリチウム元素を発光分光分析（ＩＣＰ）および酸化還元滴定により平均価数分析した結果、充電容量から算出した理論値よりもリチウム含有量が少ないことがわかったためである。つまり、初回の充電時にＬｉ２ＭｎＯ３を正極活物質として用いた正極から放出される実際のリチウムイオンは、見かけの充電容量よりも少ないことになる。したがって、負極の容量を従来よりも小さく設定しても、充放電によるリチウムの授受に影響がなく、従来と同等の充電容量が得られることがわかった。そして本発明者は、この成果を発展させることで、以降に述べる種々の発明を完成させるに至った。 The battery capacity of a lithium ion secondary battery has hitherto been thought to be caused by the movement of lithium ions. Therefore, it has been considered that the irreversible capacity is generated by the lithium ions that have moved from the positive electrode due to the charge not moving while being stored in the negative electrode. However, as a result of investigating the charge / discharge characteristics of Li 2 MnO 3 as the positive electrode active material by the present inventors, it was found that cations other than lithium ions were transferred from Li 2 MnO 3 to the negative electrode by the first charge. It was. This is because, when a lithium ion secondary battery is assembled with a positive electrode containing a positive electrode active material made of Li 2 MnO 3 and a negative electrode made of graphite, an emission spectroscopic analysis of the lithium element of the negative electrode (lithium carbide) after the first charge is performed. This is because, as a result of the average valence analysis by (ICP) and oxidation-reduction titration, it was found that the lithium content was less than the theoretical value calculated from the charge capacity. That is, the actual lithium ions released from the positive electrode using Li 2 MnO 3 as the positive electrode active material during the first charge is less than the apparent charge capacity. Therefore, it was found that even when the capacity of the negative electrode was set smaller than before, there was no effect on the exchange of lithium by charging / discharging, and a charging capacity equivalent to the conventional one could be obtained. The present inventor has developed various results described below by developing this result.

すなわち、本発明のリチウムイオン二次電池は、リチウムおよびマンガンを少なくとも含み層状岩塩構造をもつリチウム遷移金属複合酸化物を含む正極活物質を有する正極と、炭素系材料、珪素系材料および錫系材料のうちの少なくとも一種を含む負極活物質を有する負極と、非水電解液と、を備えるリチウムイオン二次電池であって、
前記リチウム遷移金属複合酸化物は不可逆容量を有し、
前記負極の金属リチウムに対する０Ｖまでの初回の充電時の単位面積当たりの実容量は、前記正極の金属リチウムに対する４．７Ｖまでの初回の充電時の単位面積当たりの実容量よりも小さいことを特徴とする。 That is, the lithium ion secondary battery of the present invention includes a positive electrode having a positive electrode active material containing a lithium transition metal composite oxide containing at least lithium and manganese and having a layered rock salt structure, a carbon-based material, a silicon-based material, and a tin-based material. A lithium ion secondary battery comprising a negative electrode having a negative electrode active material containing at least one of a nonaqueous electrolyte solution,
The lithium transition metal composite oxide has an irreversible capacity,
The actual capacity per unit area at the time of initial charging up to 0V with respect to metallic lithium of the negative electrode is smaller than the actual capacity per unit area at the time of initial charging up to 4.7V with respect to metallic lithium of the positive electrode. And

なお、本発明のリチウムイオン二次電池に用いられるリチウム遷移金属複合酸化物は、初回の充電により放出されたイオンのうち、リチウムイオンではなく、少なくとも「リチウムイオンを除く陽イオン」が負極から移動せずに不可逆容量となるために、負極の容量を従来よりも低減させても従来と同等の充電容量が得られると考えられる。「リチウムを除く陽イオン」についての詳細は不明であるが、本発明者等はプロトンであると予測している。たとえば、リチウム遷移金属複合酸化物がＬｉ２ＭｎＯ３であれば、Ｌｉ２ＭｎＯ３からリチウムとともに酸素が抜けてＬｉ２Ｏを生成すると言われており、このＬｉ２Ｏが電解液と反応して、プロトン（Ｈ＋）が生成することが推測される。このようなプロトンは、リチウムイオンよりもイオン半径が小さいため、仮に負極の容量全てが吸蔵リチウムで埋まっても、負極に吸着されたり吸着されたりしやすいと考えられる。またプロトンは、負極において水素ガス、メタンガスなどの水素含有ガスとなるため、負極に吸蔵されなくても不可逆容量となり得る。本明細書では、これ以降、上記のリチウム遷移金属複合酸化物から放出されるイオンのうち「リチウムを除く陽イオン」を、「プロトン等」と略記する。 In addition, the lithium transition metal composite oxide used in the lithium ion secondary battery of the present invention is not lithium ions, but at least “cations excluding lithium ions” move from the negative electrode among the ions released by the first charge. Therefore, even if the capacity of the negative electrode is reduced as compared with the conventional capacity, it is considered that a charge capacity equivalent to the conventional capacity can be obtained. Details of “cations other than lithium” are unknown, but the present inventors predict that they are protons. For example, if the lithium transition metal composite oxide is Li 2 MnO 3, it is said that oxygen is released from Li 2 MnO 3 together with lithium to produce Li 2 O, and this Li 2 O reacts with the electrolyte. It is estimated that protons (H + ) are generated. Since such protons have a smaller ionic radius than lithium ions, even if the entire capacity of the negative electrode is filled with occluded lithium, it is considered that such protons are easily adsorbed or adsorbed on the negative electrode. Further, since protons become hydrogen-containing gases such as hydrogen gas and methane gas in the negative electrode, they can have irreversible capacity even if they are not occluded in the negative electrode. In the present specification, among the ions released from the above lithium transition metal composite oxide, “a cation excluding lithium” is abbreviated as “proton or the like”.

ここで「実容量」とは、所定の使用状態で電池を使用したときの実際の容量値である。つまり、正極の初回充電時の「実容量」は、リチウム遷移金属複合酸化物からのリチウムイオンの放出だけでなくプロトン等の放出も加味した値である。   Here, the “actual capacity” is an actual capacity value when the battery is used in a predetermined use state. That is, the “actual capacity” at the time of the initial charge of the positive electrode is a value that considers not only the release of lithium ions from the lithium transition metal composite oxide but also the release of protons and the like.

ちなみに、特許文献１では、負極規制のリチウムイオン二次電池が開示されている。しかしながら、特許文献１のリチウムイオン二次電池は、後述の比較例２に相当する。つまり、特許文献１では、プロトン等に起因する不可逆容量を有するリチウム遷移金属複合酸化物を正極活物質として用いることは想定されていない。   Incidentally, Patent Document 1 discloses a lithium ion secondary battery regulated by a negative electrode. However, the lithium ion secondary battery of Patent Document 1 corresponds to Comparative Example 2 described later. That is, Patent Document 1 does not assume that a lithium transition metal composite oxide having an irreversible capacity caused by protons or the like is used as a positive electrode active material.

本発明のリチウムイオン二次電池は、従来よりも負極活物質の使用量を低減させても、従来と同等の容量を示すため、活物質の単位質量当たりの充放電効率が高まる。そして、負極活物質の使用量が従来よりも少なくなることで、本発明のリチウムイオン二次電池は内容量が低減され、軽量化・小型化につながる。   Since the lithium ion secondary battery of the present invention exhibits a capacity equivalent to that of the prior art even when the amount of the negative electrode active material used is reduced, the charge / discharge efficiency per unit mass of the active material is increased. And since the usage-amount of a negative electrode active material becomes smaller than before, the internal capacity of the lithium ion secondary battery of this invention is reduced, and it leads to weight reduction and size reduction.

以下に、本発明のリチウムイオン二次電池を実施するための最良の形態を説明する。なお、特に断らない限り、本明細書に記載された数値範囲「ａ〜ｂ」は、下限ａおよび上限ｂをその範囲に含む。また、その数値範囲内において、本明細書に記載した数値を任意に組み合わせることで数値範囲を構成し得る。   Below, the best form for implementing the lithium ion secondary battery of this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. In addition, the numerical range can be configured by arbitrarily combining the numerical values described in the present specification within the numerical range.

本発明のリチウムイオン二次電池は、主として、リチウムおよびマンガンを少なくとも含み層状岩塩構造をもつリチウム遷移金属複合酸化物を含む正極活物質を有する正極と、炭素系材料、珪素系材料および錫系材料のうちの少なくとも一種を含む負極活物質を有する負極と、非水電解液と、を備える。   The lithium ion secondary battery of the present invention mainly includes a positive electrode having a positive electrode active material including a lithium transition metal composite oxide containing at least lithium and manganese and having a layered rock salt structure, a carbon-based material, a silicon-based material, and a tin-based material. The negative electrode which has a negative electrode active material containing at least 1 type of these, and a non-aqueous electrolyte are provided.

前述の通り、本発明のリチウムイオン二次電池は、少なくともプロトン等（つまり、初回の充電時に対極に移動する陽イオンのうちリチウムイオンを除く陽イオン）を次回の充電時に吸蔵しない不可逆容量を有するリチウム遷移金属複合酸化物を含む正極活物質を使用する場合に、功を奏する。このような正極活物質は、リチウムおよびマンガンを少なくとも含み層状岩塩構造をもち、かつ不可逆容量を有するリチウム遷移金属複合酸化物を含む、と規定することができる。   As described above, the lithium ion secondary battery of the present invention has an irreversible capacity that does not occlude at least protons or the like (that is, cations excluding lithium ions among cations that move to the counter electrode during the first charge) during the next charge. This is effective when a positive electrode active material containing a lithium transition metal composite oxide is used. Such a positive electrode active material can be defined as including a lithium transition metal composite oxide containing at least lithium and manganese, having a layered rock salt structure, and having an irreversible capacity.

上記のリチウム遷移金属複合酸化物を組成式で表すのであれば、Ｌｉ２ＭＯ３である。Ｌｉ２ＭＯ３を基本組成とするリチウム遷移金属複合酸化物は、層状岩塩構造をもち上記のような不可逆容量を示す。このことは、Ｘ線回折、電子線回折、前述のＩＣＰ分析などを用いて確認することが可能である。組成式において、Ｍは４価のＭｎを必須とする一種以上の金属元素を表し、Ｌｉはその一部が水素で置換されてもよい。 If the above lithium transition metal composite oxide is expressed by a composition formula, it is Li 2 MO 3 . A lithium transition metal composite oxide having a basic composition of Li 2 MO 3 has a layered rock salt structure and exhibits the above irreversible capacity. This can be confirmed using X-ray diffraction, electron beam diffraction, the aforementioned ICP analysis, and the like. In the composition formula, M represents one or more metal elements essentially containing tetravalent Mn, and Li may be partially substituted with hydrogen.

なお、本明細書において「基本組成とする」とは、化学量論組成のものに限定されるわけではなく、たとえば、製造上不可避的に生じるＬｉ、ＭｎまたはＯが欠損した非化学量論組成のもの等、をも含む。上記組成式において、Ｌｉは、原子比で６０％以下さらには４５％以下が水素（Ｈ）に置換されていてもよい。また、Ｍは全て４価のマンガン（Ｍｎ）であるのが好ましいが、Ｍｎのうちの５０％未満さらには８０％未満がＭｎ以外の他の金属元素で置換されていてもよい。他の金属元素としては、電極材料とした場合の充放電可能な容量の観点から、Ｎｉ、Ａｌ、Ｃｏ、Ｆｅ、Ｍｇ、Ｔｉから選ばれるのが好ましい。   In the present specification, the “basic composition” is not limited to the stoichiometric composition. For example, a non-stoichiometric composition in which Li, Mn, or O, which is inevitably produced in production, is lost. And so on. In the above compositional formula, 60% or less, and even 45% or less of Li may be replaced with hydrogen (H) in atomic ratio. Further, all of M is preferably tetravalent manganese (Mn), but less than 50% or even less than 80% of Mn may be substituted with another metal element other than Mn. The other metal element is preferably selected from Ni, Al, Co, Fe, Mg, and Ti from the viewpoint of chargeable / dischargeable capacity when an electrode material is used.

また、正極活物質は、上記の層状岩塩構造をもつリチウム遷移金属複合酸化物（これ以下「必須のリチウム遷移金属複合酸化物」と略記）とは別に、従来からリチウムイオン二次電池の正極活物質として用いられているその他の化合物をさらに含んでもよい。具体的には、ＬｉＣｏＯ２、ＬｉＮｉ０．５Ｍｎ０．５Ｏ２、ＬｉＮｉ１／３Ｍｎ１／３Ｃｏ１／３Ｏ２、Ｌｉ４Ｍｎ５Ｏ１２、ＬｉＭｎ２Ｏ４等が挙げられる。なお、これらの化合物は、プロトン等を不可逆容量の原因とせず、不可逆容量が少ないリチウム遷移金属複合酸化物である。これらの化合物は、必須のリチウム遷移金属複合酸化物と別々に合成した後に、それらを粉末の状態で混合した混合粉末として調製してもよい。また、組み合わせによっては、これらの化合物は、必須のリチウム遷移金属複合酸化物との固溶体として合成することも可能である。 In addition to the lithium transition metal composite oxide having the layered rock salt structure (hereinafter abbreviated as “essential lithium transition metal composite oxide”), the positive electrode active material has been conventionally used in the positive electrode active of lithium ion secondary batteries. It may further contain other compounds used as substances. Specifically, LiCoO 2, LiNi 0.5 Mn 0.5 O 2, LiNi 1/3 Mn 1/3 Co 1/3 O 2, Li 4 Mn 5 O 12, LiMn 2 O 4 and the like. Note that these compounds are lithium transition metal composite oxides that do not cause protons or the like to cause irreversible capacity and have little irreversible capacity. These compounds may be prepared as a mixed powder obtained by separately synthesizing with the essential lithium transition metal composite oxide and then mixing them in a powder state. Depending on the combination, these compounds can be synthesized as a solid solution with the essential lithium transition metal composite oxide.

このとき、必須のリチウム遷移金属複合酸化物は、正極活物質を１００モル％としたときに、必須のリチウム遷移金属複合酸化物を２０モル％以上含むのが好ましい。２０モル％未満では、プロトン等（つまり、初回の充電時に対極に移動する陽イオンのうちリチウムイオンを除く陽イオン）の量が少なくなり、負極活物質の使用量を低減して正極と負極との実容量の差を大きくした場合に、負極に吸蔵可能なリチウム量を上回る量のＬｉが負極に移動する可能性がある。そのため、金属リチウムのデンドライト析出などが発生しやすくなるため好ましくない。さらに好ましい必須のリチウム遷移金属複合酸化物の含有量は、正極活物質を１００モル％としたときに、３０モル％以上さらには５０モル％以上である。   At this time, the essential lithium transition metal composite oxide preferably contains 20 mol% or more of the essential lithium transition metal composite oxide when the positive electrode active material is 100 mol%. If it is less than 20 mol%, the amount of protons (that is, cations excluding lithium ions among the cations that move to the counter electrode during the first charge) is reduced, and the amount of the negative electrode active material used is reduced. When the difference in the actual capacities is increased, there is a possibility that an amount of Li exceeding the amount of lithium that can be stored in the negative electrode moves to the negative electrode. Therefore, dendritic precipitation of metallic lithium is likely to occur, which is not preferable. A more preferable content of the essential lithium transition metal composite oxide is 30 mol% or more, further 50 mol% or more, when the positive electrode active material is 100 mol%.

負極活物質は、天然黒鉛、人造黒鉛、フェノール樹脂等の有機化合物焼成体やコークス等の炭素物質の粉状体などの炭素（Ｃ）を含む炭素系材料、珪素単体、酸化珪素、珪素化合物などの珪素（Ｓｉ）を含む珪素系材料および錫、酸化錫、錫化合物などの錫（Ｓｎ）を含む錫系材料のうちの少なくとも一種を含むのが好ましい。これらの材料は、金属リチウムに対する電極電位が低いため、本発明のリチウムイオン二次電池の負極材料として好適である。   The negative electrode active material is a carbon-based material containing carbon (C) such as a fired organic compound such as natural graphite, artificial graphite, or a phenol resin, or a powdered carbon material such as coke, silicon alone, silicon oxide, silicon compound, etc. It is preferable to include at least one of a silicon-based material containing silicon (Si) and a tin-based material containing tin (Sn) such as tin, tin oxide, and a tin compound. Since these materials have a low electrode potential with respect to metallic lithium, they are suitable as negative electrode materials for the lithium ion secondary battery of the present invention.

本発明のリチウムイオン二次電池では、負極の実容量が、正極の実容量よりも小さい。「実容量」の定義は、上述の通りである。ここで比較する正極と負極の実容量は、いずれも、対極に金属リチウムを用いた電気化学セルにおける実際の容量値とする。正極の実容量は、金属リチウムに対する４．７Ｖまでにおける初回の充電時の単位面積当たりの実際の容量値とする。負極の実容量は、金属リチウムに対する０Ｖまでにおける初回の充電時の単位面積当たりの実際の容量値とする。なお、単位面積当たりの実容量は、対極と対向する正極または負極の面積を用いて算出する。その他の条件は、正極も負極も同じ条件とするのが望ましい。その他の条件とは、電圧を除く充放電条件（電流密度など）、電気化学セルの構成（セパレータ、電解質の種類や濃度など）、正極活物質および負極活物質の含有量、測定温度、などが挙げられる。   In the lithium ion secondary battery of the present invention, the actual capacity of the negative electrode is smaller than the actual capacity of the positive electrode. The definition of “real capacity” is as described above. The actual capacities of the positive electrode and the negative electrode to be compared here are both actual capacity values in an electrochemical cell using metallic lithium as a counter electrode. The actual capacity of the positive electrode is an actual capacity value per unit area at the time of initial charge up to 4.7 V with respect to metallic lithium. The actual capacity of the negative electrode is an actual capacity value per unit area at the time of initial charge up to 0 V with respect to metallic lithium. The actual capacity per unit area is calculated using the area of the positive electrode or negative electrode facing the counter electrode. The other conditions are preferably the same for both the positive electrode and the negative electrode. Other conditions include charge / discharge conditions excluding voltage (current density, etc.), electrochemical cell configuration (separator, electrolyte type and concentration, etc.), positive and negative electrode active material contents, measurement temperature, etc. Can be mentioned.

上記の方法により得られる正極および負極の実容量は、主として、活物質の種類および活物質の含有量によって決定される、固有の値である。したがって、正極活物質と負極活物質との組み合わせ、正極活物質に含まれる必須のリチウム遷移金属複合酸化物の含有量、などを調整して負極の実容量が正極の実容量よりも小さくなるように選択するとよい。   The actual capacities of the positive electrode and negative electrode obtained by the above method are inherent values determined mainly by the type of active material and the content of active material. Therefore, the actual capacity of the negative electrode is made smaller than the actual capacity of the positive electrode by adjusting the combination of the positive electrode active material and the negative electrode active material and the content of the essential lithium transition metal composite oxide contained in the positive electrode active material. It is good to choose.

ところで、必須のリチウム遷移金属複合酸化物は、初回の充電により放出した陽イオン（リチウムイオンおよびプロトン等）のうちの３分の２（６６％）程度が充放電に寄与するリチウムイオンであると言われている。さらに、負極活物質と電解液との反応が進行し、負極表面に被膜が形成されることで、リチウムは消費される。そのため、実際に充放電に関与することができるリチウムイオンは６６％よりも少なくなる。負極の実容量は実際に充放電に関与するリチウムイオンに見合うだけあればよいため、必須のリチウム遷移金属複合酸化物のみからなる（つまり含有量が１００モル％）正極活物質であれば、負極の実容量は、正極の実容量の６２％以上、６４％以上さらには６７％以上であるとよい。また、正極活物質を１００モル％としたときに、必須のリチウム遷移金属複合酸化物を６０モル％以上含む場合、負極の実容量は、正極の実容量の７０％以上、７３％以上さらには７７％以上あるとよい。いずれの場合においても、負極の実容量を低減することで小型化および軽量化を図れるため負極の実容量が小さいほど好ましいが、正極の実容量に対して負極の実容量を小さくしすぎると、負極表面にリチウムが析出しやすくなるため望ましくない。正極の実容量に対する負極の実容量の上限を規定するのであれば、負極の実容量は、正極の実容量の１００％未満、９５％以下さらには９０％以下である。   By the way, the essential lithium transition metal complex oxide is a lithium ion in which about two thirds (66%) of cations (lithium ions, protons, etc.) released by the first charge contribute to charge / discharge. It is said. Furthermore, the reaction between the negative electrode active material and the electrolytic solution proceeds, and a film is formed on the negative electrode surface, so that lithium is consumed. Therefore, lithium ions that can actually participate in charge / discharge are less than 66%. Since the actual capacity of the negative electrode only needs to be commensurate with the lithium ions actually involved in charge and discharge, the negative electrode is composed of only the essential lithium transition metal composite oxide (ie, the content is 100 mol%). The actual capacity is preferably 62% or more, 64% or more, and further 67% or more of the actual capacity of the positive electrode. Further, when the positive electrode active material is 100 mol% and the essential lithium transition metal composite oxide is contained in an amount of 60 mol% or more, the actual capacity of the negative electrode is 70% or more, 73% or more of the actual capacity of the positive electrode. It should be 77% or more. In any case, it is preferable to reduce the actual capacity of the negative electrode because it can be reduced in size and weight by reducing the actual capacity of the negative electrode, but if the actual capacity of the negative electrode is too small relative to the actual capacity of the positive electrode, This is not desirable because lithium tends to precipitate on the negative electrode surface. If the upper limit of the actual capacity of the negative electrode with respect to the actual capacity of the positive electrode is defined, the actual capacity of the negative electrode is less than 100%, 95% or less, or 90% or less of the actual capacity of the positive electrode.

なお、必須のリチウム遷移金属複合酸化物の含有量が１００モル％未満の場合であっても、必須のリチウム遷移金属複合酸化物のみの１サイクル目の充放電効率および正極活物質に含まれるその他の化合物のみの１サイクル目の充放電効率、を測定して正極活物質に含まれるモル比に応じて比例配分することで、充放電に寄与するリチウム量および必要な負極の実容量を算出することが可能である。   In addition, even if the content of the essential lithium transition metal composite oxide is less than 100 mol%, the charge / discharge efficiency of the first cycle of only the essential lithium transition metal composite oxide and the other included in the positive electrode active material The charge / discharge efficiency in the first cycle of only the above compound is measured and proportionally distributed according to the molar ratio contained in the positive electrode active material, thereby calculating the amount of lithium contributing to charge / discharge and the required actual capacity of the negative electrode It is possible.

正極および負極は、主として、上記の活物質と、この活物質を結着する結着剤と、からなるのが好ましい。さらに、導電助材を含んでもよい。結着剤および導電助材にも特に限定はなく、一般のリチウムイオン二次電池で使用可能なものであればよい。導電助材は、電極の電気伝導性を確保するためのものであり、たとえば、カーボンブラック、アセチレンブラック、黒鉛などの炭素物質粉状体の１種または２種以上を混合したものを用いることができる。結着剤は、活物質および導電助材を繋ぎ止める役割を果たすもので、たとえば、ポリフッ化ビニリデン、ポリテトラフルオロエチレン、フッ素ゴム等の含フッ素樹脂、ポリプロピレン、ポリエチレン等の熱可塑性樹脂などを用いることができる。   The positive electrode and the negative electrode are preferably mainly composed of the above active material and a binder that binds the active material. Further, a conductive aid may be included. There are no particular limitations on the binder and the conductive additive, and any material that can be used in a general lithium ion secondary battery may be used. The conductive aid is for ensuring the electrical conductivity of the electrode, and for example, a mixture of one or more carbon material powders such as carbon black, acetylene black, and graphite may be used. it can. The binder plays a role of connecting the active material and the conductive additive. For example, a fluorine-containing resin such as polyvinylidene fluoride, polytetrafluoroethylene or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene is used. be able to.

正極および負極は、少なくとも正極活物質または負極活物質が結着剤で結着されてなる活物質層が、集電体に付着してなるのが一般的である。そのため、正極および負極は、活物質および結着剤、必要に応じて導電助材を含む電極合材層形成用組成物を調製し、さらに適当な溶剤を加えてペースト状にしてから集電体の表面に塗布後、乾燥し、必要に応じて電極密度を高めるべく圧縮して形成することができる。   The positive electrode and the negative electrode generally have an active material layer formed by binding at least a positive electrode active material or a negative electrode active material with a binder attached to a current collector. Therefore, a positive electrode and a negative electrode are prepared by preparing an electrode mixture layer forming composition containing an active material, a binder, and, if necessary, a conductive additive, and further adding a suitable solvent to make a paste, After coating on the surface of the film, it can be dried and, if necessary, compressed to increase the electrode density.

集電体は、金属製のメッシュや金属箔を用いることができる。集電体としては、ステンレス鋼、チタン、ニッケル、アルミニウム、銅などの金属材料または導電性樹脂からなる多孔性または無孔の導電性基板が挙げられる。多孔性導電性基板としては、たとえば、メッシュ体、ネット体、パンチングシート、ラス体、多孔質体、発泡体、不織布などの繊維群成形体、などが挙げられる。無孔の導電性基板としては、たとえば、箔、シート、フィルムなどが挙げられる。電極合材層形成用組成物の塗布方法としては、ドクターブレード、バーコーターなどの従来から公知の方法を用いればよい。   A metal mesh or metal foil can be used for the current collector. Examples of the current collector include a porous or non-porous conductive substrate made of a metal material such as stainless steel, titanium, nickel, aluminum, or copper, or a conductive resin. Examples of the porous conductive substrate include a mesh body, a net body, a punching sheet, a lath body, a porous body, a foamed body, a fiber group molded body such as a nonwoven fabric, and the like. Examples of the non-porous conductive substrate include a foil, a sheet, and a film. As a method for applying the composition for forming an electrode mixture layer, a conventionally known method such as a doctor blade or a bar coater may be used.

粘度調整のための溶剤としては、Ｎ−メチル−２−ピロリドン（ＮＭＰ）、メタノール、メチルイソブチルケトン（ＭＩＢＫ）などが使用可能である。   As a solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

電解質としては、有機溶媒に電解質を溶解させた有機溶媒系の電解液や、電解液をポリマー中に保持させたポリマー電解質などを用いることができる。その電解液あるいはポリマー電解質に含まれる有機溶媒は特に限定されるものではないが、負荷特性の点からは鎖状エステルを含んでいることが好ましい。そのような鎖状エステルとしては、たとえば、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネートに代表される鎖状のカーボネートや、酢酸エチル、プロピロン酸メチルなどの有機溶媒が挙げられる。これらの鎖状エステルは、単独でもあるいは２種以上を混合して用いてもよく、特に、低温特性の改善のためには、上記鎖状エステルが全有機溶媒中の５０体積％以上を占めることが好ましく、特に鎖状エステルが全有機溶媒中の６５体積％以上を占めることが好ましい。   As the electrolyte, an organic solvent-based electrolytic solution in which an electrolyte is dissolved in an organic solvent, a polymer electrolyte in which an electrolytic solution is held in a polymer, or the like can be used. The organic solvent contained in the electrolytic solution or polymer electrolyte is not particularly limited, but it preferably contains a chain ester from the viewpoint of load characteristics. Examples of such chain esters include chain carbonates typified by dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and organic solvents such as ethyl acetate and methyl propionate. These chain esters may be used alone or in admixture of two or more. Particularly, for improving low-temperature characteristics, the above-mentioned chain esters occupy 50% by volume or more in the total organic solvent. In particular, it is preferable that the chain ester occupies 65% by volume or more of the total organic solvent.

ただし、有機溶媒としては、上記鎖状エステルのみで構成するよりも、放電容量の向上をはかるために、上記鎖状エステルに誘導率の高い（誘導率：３０以上）エステルを混合して用いることが好ましい。このようなエステルの具体例としては、たとえば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ビニレンカーボネートに代表される環状のカーボネートや、γ−ブチロラクトン、エチレングリコールサルファイトなどが挙げられ、特にエチレンカーボネート、プロピレンカーボネートなどの環状構造のエステルが好ましい。そのような誘電率の高いエステルは、放電容量の点から、全有機溶媒中１０体積％以上、特に２０体積％以上含有されることが好ましい。また、負荷特性の点からは、４０体積％以下が好ましく、３０体積％以下がより好ましい。   However, as an organic solvent, in order to improve the discharge capacity, rather than using only the above chain ester, an ester having a high induction rate (induction rate: 30 or more) is mixed with the chain ester. Is preferred. Specific examples of such esters include, for example, cyclic carbonates represented by ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, ethylene glycol sulfite, and the like. A cyclic ester such as carbonate is preferred. Such an ester having a high dielectric constant is preferably contained in an amount of 10% by volume or more, particularly 20% by volume or more in the total organic solvent from the viewpoint of discharge capacity. Moreover, from the point of load characteristics, 40 volume% or less is preferable and 30 volume% or less is more preferable.

有機溶媒に溶解させる電解質としては、たとえば、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＣＦ３ＣＯ２、Ｌｉ２Ｃ２Ｆ４（ＳＯ３）２、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣnＦ２ｎ＋１ＳＯ３（ｎ≧２）などが単独でまたは２種以上混合して用いられる。中でも、良好な充放電特性が得られるＬｉＰＦ６やＬｉＣ４Ｆ９ＳＯ３などが好ましく用いられる。 As an electrolyte to be dissolved in an organic solvent, for example, LiClO 4, LiPF 6, LiBF 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 ( SO 3 ) 2 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3 , LiCnF 2n + 1 SO 3 (n ≧ 2) are used alone or in combination. Among these, LiPF 6 and LiC 4 F 9 SO 3 that can obtain good charge / discharge characteristics are preferably used.

電解液中における電解質の濃度は、特に限定されるものではないが、０．３〜１．７ｍｏｌ／ｄｍ３、特に０．４〜１．５ｍｏｌ／ｄｍ３程度が好ましい。 The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably about 0.3 to 1.7 mol / dm 3 , particularly about 0.4 to 1.5 mol / dm 3 .

また、電池の安全性や貯蔵特性を向上させるために、非水電解液に芳香族化合物を含有させてもよい。芳香族化合物としては、シクロヘキシルベンゼンやｔ−ブチルベンゼンなどのアルキル基を有するベンゼン類、ビフェニル、あるいはフルオロベンゼン類が好ましく用いられる。   Moreover, in order to improve the safety | security and storage characteristic of a battery, you may make an non-aqueous electrolyte contain an aromatic compound. As the aromatic compound, benzenes having an alkyl group such as cyclohexylbenzene or t-butylbenzene, biphenyl, or fluorobenzenes are preferably used.

本発明のリチウムイオン二次電池は、一般のリチウムイオン二次電池と同様に、正極と負極の間に挟装されるセパレータを備えるとよい。   The lithium ion secondary battery of this invention is good to provide the separator pinched | interposed between a positive electrode and a negative electrode similarly to a general lithium ion secondary battery.

セパレータとしては、強度が充分でしかも電解液を多く保持できるものがよく、そのような観点から、５〜５０μｍの厚さで、ポリプロピレン製、ポリエチレン製、プロピレンとエチレンとの共重合体などポリオレフィン製の微孔性フィルムや不織布などが好ましく用いられる。   As the separator, a separator having sufficient strength and capable of holding a large amount of electrolyte solution is preferable. From such a viewpoint, the separator is made of polyolefin such as polypropylene, polyethylene, a copolymer of propylene and ethylene, with a thickness of 5 to 50 μm. A microporous film or non-woven fabric is preferably used.

本発明のリチウムイオン二次電池の形状は円筒型、積層型、コイン型等、種々のものとすることができる。いずれの形状を採る場合であっても、正極と負極との間にセパレータを挟装させ電極体とする。そして正極集電体および負極集電体から外部に通ずる正極端子および負極端子までの間を集電用リードなどで接続し、この電極体に上記電解液を含浸させ電池ケースに密閉し、リチウムイオン二次電池が完成する。   The lithium ion secondary battery of the present invention can have various shapes such as a cylindrical shape, a stacked shape, and a coin shape. In any case, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. Then, the positive electrode current collector and the negative electrode current collector are connected to the positive electrode terminal and the negative electrode terminal communicating with the outside with a current collecting lead, etc., and the electrode body is impregnated with the above electrolyte solution and hermetically sealed in a battery case. A secondary battery is completed.

リチウムイオン二次電池を使用する場合には、はじめに充電を行い、正極活物質を活性化させる。ただし、上記の複合酸化物を正極活物質として用いる場合には、初回の充電時にリチウムイオンの放出とともに酸素が発生する。そのため、電池ケースを密閉する前に充電を行うのが望ましい。   When using a lithium ion secondary battery, it charges first and activates a positive electrode active material. However, when the composite oxide is used as a positive electrode active material, oxygen is generated along with the release of lithium ions during the first charge. For this reason, it is desirable to charge the battery case before sealing it.

本発明のリチウムイオン二次電池は、携帯電話、パソコン等の通信機器、情報関連機器の分野の他、自動車の分野においても好適に利用できる。たとえば、このリチウムイオン二次電池を車両に搭載すれば、リチウムイオン二次電池を電気自動車用の電源として使用できる。   The lithium ion secondary battery of the present invention can be suitably used in the field of automobiles in addition to the fields of communication devices such as mobile phones and personal computers and information-related devices. For example, if this lithium ion secondary battery is mounted on a vehicle, the lithium ion secondary battery can be used as a power source for an electric vehicle.

以上、本発明のリチウムイオン二次電池の実施形態を説明したが、本発明は、上記実施形態に限定されるものではない。本発明の要旨を逸脱しない範囲において、当業者が行い得る変更、改良等を施した種々の形態にて実施することができる。   As mentioned above, although embodiment of the lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

以下に、本発明のリチウムイオン二次電池の実施例を挙げて、本発明を具体的に説明する。   Hereinafter, the present invention will be specifically described with reference to examples of the lithium ion secondary battery of the present invention.

〔負極の作製〕
負極活物質としてグラファイトを含む負極を作製した。 (Production of negative electrode)
A negative electrode containing graphite as a negative electrode active material was produced.

グラファイトとアセチレンブラック（導電助剤）とポリフッ化ビニリデン（結着剤）とを質量比で９２：３：５となるように混合した。これを、Ｎ−メチル−２−ピロリドン（ＮＭＰ）に分散させてスラリーを得た。このスラリーを集電体である銅箔（厚さ１０μｍ）に塗布し、１２０℃で１２時間以上真空乾燥した。乾燥後プレスし、直径１６ｍｍφに打ち抜き、負極とした。なお、スラリーの塗布量は、負極活物質換算で９ｍｇ／ｃｍ２であった。 Graphite, acetylene black (conducting aid), and polyvinylidene fluoride (binder) were mixed at a mass ratio of 92: 3: 5. This was dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a slurry. This slurry was applied to a copper foil (thickness 10 μm) as a current collector and vacuum-dried at 120 ° C. for 12 hours or more. After drying, it was pressed and punched out to a diameter of 16 mmφ to obtain a negative electrode. In addition, the application quantity of the slurry was 9 mg / cm < 2 > in conversion of the negative electrode active material.

得られた電極について、金属リチウムを対極として電気化学セルを作製し、０Ｖから１．２Ｖの電圧範囲における電極容量（実容量）を測定した。なお、電解液としてエチレンカーボネートとエチルメチルカーボネートとを体積比１：２の混合溶媒にＬｉＰＦ６を１．０ｍｏｌ／Ｌ溶解させてなる非水電解液を用い、セパレータとして厚さ２０μｍの微孔性ポリエチレンフィルムを両電極間に配置して、電気化学セル作製した。この電気化学セルを用い、３０℃一定温度下において０．２Ｃの条件で充放電試験を行った。その結果、この電極の初回の充電容量は、負極活物質の単位質量当たり３５５ｍＡｈ／ｇ（負極の単位面積当たり３．０ｍＡｈ／ｃｍ２）であった。 About the obtained electrode, the electrochemical cell was produced using metallic lithium as a counter electrode, and the electrode capacity (actual capacity) in the voltage range of 0V to 1.2V was measured. In addition, a non-aqueous electrolyte obtained by dissolving 1.0 mol / L of LiPF 6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 2 is used as an electrolyte, and a microporous material having a thickness of 20 μm is used as a separator. A polyethylene film was placed between both electrodes to produce an electrochemical cell. Using this electrochemical cell, a charge / discharge test was conducted at a constant temperature of 30 ° C. under the condition of 0.2C. As a result, the initial charge capacity of this electrode was 355 mAh / g per unit mass of the negative electrode active material (3.0 mAh / cm 2 per unit area of the negative electrode).

〔正極の作製〕
正極活物質としてＬｉ２ＭｎＯ３を含む正極を作製した。 [Production of positive electrode]
A positive electrode containing Li 2 MnO 3 as a positive electrode active material was produced.

平均一次粒子径２００ｎｍのＬｉ２ＭｎＯ３を準備した。Ｌｉ２ＭｎＯ３とアセチレンブラックとポリフッ化ビニリデンとを質量比で８０：１０：１０となるように混合した。これを、ＮＭＰに分散させてスラリーを得た。このスラリーを集電体であるアルミニウム箔（厚さ１５μｍ）に塗布し、１２０℃で１２時間以上真空乾燥した。乾燥後プレスし、直径１６ｍｍφに打ち抜き、正極とした。なお、電極の塗布重量は、負極活物質換算で５ｍｇ／ｃｍ２または１０ｍｇ／ｃｍ２とし、二種類の正極＃０１および＃０２とした。 Li 2 MnO 3 having an average primary particle diameter of 200 nm was prepared. Li 2 MnO 3 , acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 80:10:10. This was dispersed in NMP to obtain a slurry. This slurry was applied to an aluminum foil (thickness 15 μm) as a current collector and vacuum-dried at 120 ° C. for 12 hours or more. After drying, it was pressed and punched out to a diameter of 16 mmφ to obtain a positive electrode. The coating weight of the electrode, a 5 mg / cm 2 or 10 mg / cm 2 in the negative electrode active material terms, and the two kinds of cathode # 01 and # 02.

また、正極活物質としてＬｉ２ＭｎＯ３に換えて０．６Ｌｉ２ＭｎＯ３−０．２ＬｉＮｉ０．５Ｍｎ０．５Ｏ２−０．２ＬｉＮｉ１／３Ｍｎ１／３Ｃｏ１／３Ｏ２、０．６Ｌｉ２ＭｎＯ３−０．４Ｌｉ４Ｍｎ５Ｏ１２、０．３Ｌｉ２ＭｎＯ３−０．７ＬｉＮｉ０．５Ｍｎ０．５Ｏ２またはＬｉＮｉ０．５Ｍｎ０．５Ｏ２（いずれも平均一次粒子径２００ｎｍ）を含む正極＃０３〜＃０６を、上記と同様の手順で作製した。つまり、＃０１および＃０２は正極活物質として充電時にリチウム以外のイオンを放出するＬｉ２ＭｎＯ３を１００ｍｏｌ％含み、＃０３および＃０４は６０ｍｏｌ％、＃０５は３０ｍｏｌ％、＃０６はＬｉ２ＭｎＯ３を含まない正極とした。 Further, 0.6Li 2 MnO 3 -0.2LiNi 0.5 Mn 0.5 O 2 -0.2LiNi 1/3 Mn 1/3 Co 1/3 O 2 in place of the Li 2 MnO 3 as a positive electrode active material, 0.6Li 2 MnO 3 -0.4Li 4 Mn 5 O 12, 0.3Li 2 MnO 3 -0.7LiNi 0.5 Mn 0.5 O 2 or LiNi 0.5 Mn 0.5 O 2 (average both Positive electrodes # 03 to # 06 including a primary particle diameter of 200 nm were prepared in the same procedure as described above. That is, # 01 and # 02 contain 100 mol% of Li 2 MnO 3 that releases ions other than lithium as a positive electrode active material when charged, # 03 and # 04 are 60 mol%, # 05 is 30 mol%, and # 06 is Li 2. A positive electrode containing no MnO 3 was obtained.

それぞれの電極について、金属リチウムを対極として電気化学セルを作製し、４．７Ｖから２．０Ｖの電圧範囲における電極容量を測定した。なお、電解液としてエチレンカーボネートとエチルメチルカーボネートとを体積比１：２の混合溶媒にＬｉＰＦ６を１．０ｍｏｌ／Ｌ溶解させてなる非水電解液を用い、セパレータとして厚さ２０μｍの微孔性ポリエチレンフィルムを両電極間に配置して、電気化学セルを作製した。この電気化学セルを用い、３０℃一定温度下において０．２Ｃの条件で定電流定電圧充電−定電流放電充放電試験を行った。充放電試験より得られた正極の初回の充電容量およびその後の放電容量（つまり１サイクル目の充放電容量）を、正極活物質の単位質量当たり、および正極の単位面積当たりで、それぞれ表１に示した。 For each electrode, an electrochemical cell was prepared using metallic lithium as a counter electrode, and the electrode capacity in a voltage range of 4.7 V to 2.0 V was measured. In addition, a non-aqueous electrolyte obtained by dissolving 1.0 mol / L of LiPF 6 in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 2 is used as an electrolyte, and a microporous material having a thickness of 20 μm is used as a separator. A polyethylene film was placed between both electrodes to produce an electrochemical cell. Using this electrochemical cell, a constant current / constant voltage charge / constant current discharge charge / discharge test was conducted at a constant temperature of 30 ° C. under the condition of 0.2C. The initial charge capacity and subsequent discharge capacity of the positive electrode obtained from the charge / discharge test (that is, the charge / discharge capacity at the first cycle) are shown in Table 1 per unit mass of the positive electrode active material and per unit area of the positive electrode, respectively. Indicated.

Figure 2011228052
Figure 2011228052

これ以下、負極および正極の１サイクル目の充電容量を、それぞれ、正極および負極の「実容量」、と記載する。   Hereinafter, the first cycle charge capacities of the negative electrode and the positive electrode are referred to as “actual capacities” of the positive electrode and the negative electrode, respectively.

表１より、＃０１および＃０２の正極活物質は、その充放電効率から、充電容量の約３８％が不可逆容量であることがわかった。＃０１および＃０２の正極活物質はＬｉ２ＭｎＯ３が１００モル％であったが、Ｌｉ２ＭｎＯ３の含有割合が少ない＃０３〜＃０５の正極活物質では、Ｌｉ２ＭｎＯ３の含有割合が少ないほど不可逆容量が減少した。 From Table 1, it was found that about 38% of the charge capacity of the # 01 and # 02 positive electrode active materials was irreversible capacity from the charge and discharge efficiency. # 01 and although the positive electrode active material of # 02 are Li 2 MnO 3 was 100 mol%, in the positive electrode active material of Li 2 MnO 3 of the content is less # 03～ # 05, the content of Li 2 MnO 3 The less irreversible capacity decreased.

〔リチウムイオン二次電池の作製〕
〔実施例１〕
上記の負極（実容量：３．０ｍＡｈ／ｃｍ２）と正極＃０２（実容量：４．２ｍＡｈ／ｃｍ２）とを組み合わせてコイン型のリチウムイオン二次電池を作製した。電解液としてエチレンカーボネートとエチルメチルカーボネートとを体積比１：２で混合した混合溶媒にＬｉＰＦ６を１．０ｍｏｌ／Ｌ溶解させてなる非水電解液を用い、セパレータとして厚さ２０μｍの微孔性ポリエチレンフィルムを両電極間に配置した。 [Production of lithium ion secondary battery]
[Example 1]
A coin-type lithium ion secondary battery was fabricated by combining the above negative electrode (actual capacity: 3.0 mAh / cm 2 ) and positive electrode # 02 (actual capacity: 4.2 mAh / cm 2 ). A non-aqueous electrolyte obtained by dissolving 1.0 mol / L of LiPF 6 in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2 was used as the electrolyte, and the separator was microporous with a thickness of 20 μm. A polyethylene film was placed between the electrodes.

〔実施例２〕
上記の負極（実容量：３．０ｍＡｈ／ｃｍ２）と正極＃０３（実容量：３．８ｍＡｈ／ｃｍ２）とを組み合わせてリチウムイオン二次電池を作製した。 [Example 2]
A lithium ion secondary battery was fabricated by combining the above negative electrode (actual capacity: 3.0 mAh / cm 2 ) and positive electrode # 03 (actual capacity: 3.8 mAh / cm 2 ).

〔実施例３〕
上記の負極（実容量：３．０ｍＡｈ／ｃｍ２）と正極＃０４（実容量：３．２５ｍＡｈ／ｃｍ２）とを組み合わせてリチウムイオン二次電池を作製した。 Example 3
A lithium ion secondary battery was fabricated by combining the above negative electrode (actual capacity: 3.0 mAh / cm 2 ) and positive electrode # 04 (actual capacity: 3.25 mAh / cm 2 ).

〔実施例４〕
上記の負極（実容量：３．０ｍＡｈ／ｃｍ２）と正極＃０５（実容量：３．６ｍＡｈ／ｃｍ２）とを組み合わせてリチウムイオン二次電池を作製した。 Example 4
A lithium ion secondary battery was fabricated by combining the above negative electrode (actual capacity: 3.0 mAh / cm 2 ) and positive electrode # 05 (actual capacity: 3.6 mAh / cm 2 ).

〔比較例１〕
上記の負極（実容量：３．０ｍＡｈ／ｃｍ２）と正極＃０１（実容量：２．１ｍＡｈ／ｃｍ２）とを組み合わせてリチウムイオン二次電池を作製した。 [Comparative Example 1]
A lithium ion secondary battery was fabricated by combining the above negative electrode (actual capacity: 3.0 mAh / cm 2 ) and positive electrode # 01 (actual capacity: 2.1 mAh / cm 2 ).

〔比較例２〕
上記の負極（実容量：３．０ｍＡｈ／ｃｍ２）とＬｉ２ＭｎＯ３を含まない正極＃０６（実容量：３．２ｍＡｈ／ｃｍ２）とを組み合わせてリチウムイオン二次電池を作製した。 [Comparative Example 2]
A lithium ion secondary battery was fabricated by combining the above negative electrode (actual capacity: 3.0 mAh / cm 2 ) and positive electrode # 06 (actual capacity: 3.2 mAh / cm 2 ) not including Li 2 MnO 3 .

〔評価〕
〔リチウムイオン二次電池の充放電試験〕
上記の各リチウムイオン二次電池を用いて、３０℃の一定温度の下、４．６Ｖから１．９Ｖの範囲で０．２Ｃのレートにおいて定電流・定電圧充電−定電流放電充放電試験を行った。充放電試験より得られた初回の充電容量およびその後の放電容量（つまり１サイクル目の充放電容量）を、正極活物質の単位質量当たり、および正極の単位面積当たりで、それぞれ表２に示した。 [Evaluation]
[Charge / discharge test of lithium ion secondary battery]
Using each of the above lithium ion secondary batteries, a constant current / constant voltage charge-constant current discharge charge / discharge test was performed at a constant temperature of 30 ° C. and a rate of 0.2 C in the range of 4.6 V to 1.9 V went. The initial charge capacity and the subsequent discharge capacity (that is, the charge / discharge capacity at the first cycle) obtained from the charge / discharge test are shown in Table 2 per unit mass of the positive electrode active material and per unit area of the positive electrode. .

また、実施例１のリチウムイオン二次電池に対しては、３０℃の一定温度の下、４．５Ｖから１．９Ｖまたは４．０Ｖから１．９Ｖの範囲で０．２Ｃのレートにおいて定電流・定電圧充電−定電流放電充放電試験を行った。１サイクル目の充電容量および放電容量を表２に示した。   For the lithium ion secondary battery of Example 1, a constant current at a rate of 0.2 C in the range of 4.5 V to 1.9 V or 4.0 V to 1.9 V at a constant temperature of 30 ° C. -A constant voltage charge-constant current discharge charge / discharge test was conducted. The charge capacity and discharge capacity at the first cycle are shown in Table 2.

Figure 2011228052
Figure 2011228052

実施例１のリチウムイオン二次電池では、３．０ｍＡｈ／ｃｍ２の実容量をもつ負極と４．２ｍＡｈ／ｃｍ２の実容量をもつ正極＃０２とを組み合わせて用いた。つまり、この二次電池は、負極の実容量が正極の実容量よりも小さくなるように構成されていた。一方、比較例１のリチウムイオン二次電池は、実施例１と同じ負極を用いているが、正極の実容量が負極の実容量よりも小さくなるように構成されていた。しかし、これらの二次電池において、正極活物質の単位質量当たりの充放電容量に差は生じなかった。つまり、実施例１のリチウムイオン二次電池は、負極の実容量を低減しても、比較例１のような従来のリチウムイオン二次電池と同等の性能が発揮されることが確認できた。 The lithium ion secondary battery of Example 1, using the combination of a positive electrode # 02 with a real capacity of the negative electrode and 4.2mAh / cm 2 with a real capacity of 3.0 mAh / cm 2. That is, the secondary battery is configured such that the actual capacity of the negative electrode is smaller than the actual capacity of the positive electrode. On the other hand, the lithium ion secondary battery of Comparative Example 1 uses the same negative electrode as in Example 1, but is configured such that the actual capacity of the positive electrode is smaller than the actual capacity of the negative electrode. However, in these secondary batteries, there was no difference in charge / discharge capacity per unit mass of the positive electrode active material. That is, it was confirmed that the lithium ion secondary battery of Example 1 exhibited the same performance as the conventional lithium ion secondary battery as in Comparative Example 1 even when the actual capacity of the negative electrode was reduced.

また、実施例１のリチウムイオン二次電池では、正極活物質としてＬｉ２ＭｎＯ３を使用した。一方、比較例２のリチウムイオン二次電池では、正極活物質としてＬｉＮｉ０．５Ｍｎ０．５Ｏ２を使用した。いずれの二次電池も、負極の実容量が正極の実容量よりも小さくなるように構成されているが、実施例１の二次電池では正極の実容量に近い充電容量、比較例２の二次電池では負極の実容量に近い充電容量、を示した。換言すれば、リチウムイオン二次電池の充電容量は、実施例１では正極規制、比較例２では負極規制、であった。つまり、正極活物質がＬｉ２ＭｎＯ３であれば、正極の実容量よりも負極の実容量を小さくしても正極の実容量の全てを充電可能である点において、従来のリチウムイオン二次電池と大きく異なった。 In the lithium ion secondary battery of Example 1, Li 2 MnO 3 was used as the positive electrode active material. On the other hand, in the lithium ion secondary battery of Comparative Example 2, LiNi 0.5 Mn 0.5 O 2 was used as the positive electrode active material. Each of the secondary batteries is configured such that the actual capacity of the negative electrode is smaller than the actual capacity of the positive electrode. However, in the secondary battery of Example 1, the charge capacity close to the actual capacity of the positive electrode, The secondary battery showed a charge capacity close to the actual capacity of the negative electrode. In other words, the charge capacity of the lithium ion secondary battery was positive electrode regulation in Example 1 and negative electrode regulation in Comparative Example 2. That is, if the positive electrode active material is Li 2 MnO 3 , the conventional lithium ion secondary battery can be charged even if the actual capacity of the negative electrode is made smaller than the actual capacity of the positive electrode. It was very different.

また、実施例２〜４のリチウムイオン二次電池においても、実施例１のリチウムイオン二次電池と同様に、負極の実容量よりも大きな正極の実容量の電池を構成しても、充電容量が大きく低下せず、また放電容量も負極表面に形成される皮膜に消費されるＬｉの量を考慮すると大きな容量の低下は無いと考えられた。   In addition, in the lithium ion secondary batteries of Examples 2 to 4, as with the lithium ion secondary battery of Example 1, even if a battery having a positive capacity larger than the actual capacity of the negative electrode is configured, the charge capacity In view of the amount of Li consumed in the film formed on the negative electrode surface, it was considered that there was no significant decrease in capacity.

すなわち、実施例１〜４のリチウムイオン二次電池は、負極の実容量が正極の実容量より小さいにもかかわらず、充放電効率において、比較例１のリチウムイオン二次電池と大差は無かった。これは、Ｌｉ２ＭｎＯ３を含む正極活物質から初回の充電の際に対極に移動するリチウムイオンは、正極の実容量に満たない量であったことを示す。負極の実容量が正極の実容量よりも小さいにもかかわらず充電容量の値が大きかったのは、充電過程においてプロトン等が発生し、それがリチウムとともに負極に移動したためと考えられる。 That is, the lithium ion secondary batteries of Examples 1 to 4 were not much different from the lithium ion secondary battery of Comparative Example 1 in charge / discharge efficiency, although the actual capacity of the negative electrode was smaller than the actual capacity of the positive electrode. . This indicates that the amount of lithium ions moving from the positive electrode active material containing Li 2 MnO 3 to the counter electrode during the first charge was less than the actual capacity of the positive electrode. The reason why the value of the charge capacity was large even though the actual capacity of the negative electrode was smaller than the actual capacity of the positive electrode is thought to be that protons and the like were generated during the charging process and moved to the negative electrode together with lithium.

実施例１のリチウムイオン二次電池において、充放電電圧の上限を変化させても、充放電効率に大きな変化はなかった。すなわち、実施例１のリチウムイオン二次電池は、いずれの電圧範囲においても、充電された容量を全て放出することができないことがわかった。この結果から、負極の実容量を超える充電容量は、従来のリチウムイオン二次電池において起こりうる過剰な充電による電解液の分解によるものではなく、上記のように、充電過程においてリチウムイオンとともにプロトン等のＬｉイオン以外の陽イオンが移動したためであることがわかった。   In the lithium ion secondary battery of Example 1, there was no significant change in charge / discharge efficiency even when the upper limit of the charge / discharge voltage was changed. That is, it was found that the lithium ion secondary battery of Example 1 could not discharge all charged capacity in any voltage range. From this result, the charge capacity exceeding the actual capacity of the negative electrode is not due to decomposition of the electrolyte due to excessive charging that can occur in the conventional lithium ion secondary battery, but as described above, protons etc. together with lithium ions in the charging process It was found that cations other than Li ions moved.

Claims (7)

リチウムおよびマンガンを少なくとも含み層状岩塩構造をもつリチウム遷移金属複合酸化物を含む正極活物質を有する正極と、炭素系材料、珪素系材料および錫系材料のうちの少なくとも一種を含む負極活物質を有する負極と、非水電解液と、を備えるリチウムイオン二次電池であって、
前記リチウム遷移金属複合酸化物は不可逆容量を有し、
前記負極の金属リチウムに対する０Ｖまでの初回の充電時の単位面積当たりの実容量は、前記正極の金属リチウムに対する４．７Ｖまでの初回の充電時の単位面積当たりの実容量よりも小さいことを特徴とするリチウムイオン二次電池。 A positive electrode having a positive electrode active material containing at least lithium and manganese and including a lithium transition metal composite oxide having a layered rock salt structure; and a negative electrode active material containing at least one of a carbon-based material, a silicon-based material, and a tin-based material A lithium ion secondary battery comprising a negative electrode and a non-aqueous electrolyte,
The lithium transition metal composite oxide has an irreversible capacity,
The actual capacity per unit area at the time of initial charging up to 0V with respect to metallic lithium of the negative electrode is smaller than the actual capacity per unit area at the time of initial charging up to 4.7V with respect to metallic lithium of the positive electrode. Lithium ion secondary battery. 前記リチウム遷移金属複合酸化物は、少なくとも、初回の充電時に放出する陽イオンのうちリチウムイオンを除く陽イオンを、次回の充電時に吸蔵しない不可逆容量を有する請求項１記載のリチウムイオン二次電池。   2. The lithium ion secondary battery according to claim 1, wherein the lithium transition metal composite oxide has an irreversible capacity that does not occlude at least a cation other than a lithium ion among cations released at the first charge during the next charge. 前記リチウム遷移金属複合酸化物は、組成式：Ｌｉ２ＭＯ３（ＭはＭｎを必須とする一種以上の金属元素、Ｌｉはその一部が水素で置換されてもよい）で表される請求項１または２に記載のリチウムイオン二次電池。 The lithium transition metal composite oxide is represented by a composition formula: Li 2 MO 3 (M is one or more metal elements in which Mn is essential, and Li may be partially substituted with hydrogen). The lithium ion secondary battery according to 1 or 2. 前記リチウム遷移金属複合酸化物は、Ｌｉ２ＭｎＯ３である請求項３記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 3 , wherein the lithium transition metal composite oxide is Li 2 MnO 3 . 前記正極活物質は、該正極活物質を１００モル％としたときに前記リチウム遷移金属複合酸化物を２０モル％以上含む請求項１〜４のいずれかに記載のリチウムイオン二次電池。   The lithium ion secondary battery according to any one of claims 1 to 4, wherein the positive electrode active material contains 20 mol% or more of the lithium transition metal composite oxide when the positive electrode active material is 100 mol%. 前記負極活物質は、炭素系材料である請求項１〜５のいずれかに記載のリチウムイオン二次電池。   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material is a carbon-based material. 請求項１〜６のいずれかに記載のリチウムイオン二次電池を搭載したことを特徴とする車両。   A vehicle comprising the lithium ion secondary battery according to claim 1.
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